Currently, various curable liquid compositions have been developed, which can form rubber-like materials by curing. Especially, silicone rubber using hydrosilylation addition reaction as cross-linking reaction is excellent in weather resistance, heat resistance, water resistance; and further it has such characteristic properties that shape change thereof due to its curing reaction is small before and after curing, that an energy consumption is small because of quick-curing at a high temperature and that it is quite safe. This silicone rubber is used as a silicone sealing material and a potting material. However, its use is limited for such reasons that the cost of this curing system is high, its adhesion is poor, it easily gets moldy, and the like.
On the other hand, as a curing system which do not use such an expensive organopolysiloxane, Japanese Kokai Publication Hei-2-75644 and Japanese Kokai Publication Hei-3-181565 have disclosed a curable composition characterized in that a polymer having at least one alkenyl group in a molecule is cross-linked by a hydrocarbon curing agent having two hydrogen atoms bonded to silicon atom in a molecule.
Among these, the curable composition characterized in that the above-mentioned polymer comprises an isobutylene polymer of a saturated hydrocarbon is excellent in low moisture permeability, low gas permeability, chemical resistance and high vibration damping property, etc., in addition to weather resistance and heat resistance while these excellent properties can not be simultaneously realized in the above-mentioned silicone systems. Thus, wide uses thereof can be expected.
However, when this isobutylene polymer is treated as a liquid composition, it sometimes becomes necessary that the viscosity of its resin component be made low in order to blend various additives and fillers because of its high viscosity.
As general means, a non-reactive plasticizer including a process oil is used. Because these plasticizers are non-reactive, they can not be built in cross-linking, and large lowering of various characteristics such as mechanical property and heat resistance is inevitable by addition of these plasticizers. There is also the drawback that the plasticizers evaporate at a high temperature, and in particular from a point of view of heat resistance, its improvement is desired.